1. Field:
This invention generally relates to oxygen generating devices and particularly to electrochemical oxygen generating devices using a solid oxygen ion conducting electrolyte composed of a metal oxide ceramic material.
2. Prior Art:
Electrochemical devices which employ oxygen ion conducting electrolytes are well known. Such devices are used as sensors whereby the oxygen partial pressure difference existing between opposite sides of said electrolyte create a voltage potential which may be determined to indicate a level of oxygen concentration on one side or the other, especially when the oxygen concentration on one side of the sensor is known. Such sensors are used in automobile engines, furnaces and other devices wherein it is desired to operate at stoichiometric ratios between the fuel and the air or oxygen necessary for combustion of fuel.
Also, such electrochemical devices, when operated in a current mode with an applied voltage may be utilized to generate pure oxygen. Devices of this type are discussed in certain patents to Ruka.
Certain difficulties have generally been encountered with such oxygen sensors and oxygen generating devices. In electrochemical sensors it is common practice to utilize platinum as an electrode or to utilize various electrode layers, for example, a platinum electrode adjacent to the electrolyte with an overcoating of a protective porous film. Platinum has been generally employed because of its catalytic activity and because of its relatively high melting point among conductive metals. It has been found, however, in oxygen generating electrochemical cells that platinum, which is relatively conductive, has an apparent resistance which is much higher than what would normally be expected. Thus, oxygen generating electrochemical cells utilizing platinum electrodes have been electrically inefficient. Furthermore, platinum electrodes must be porous in order to permit oxygen molecules to pass physically through the electrode layer, to reach the surface of the electrolyte (cathode), and, upon recombination at the anode surface, to depart from the electrolyte surface and physically pass through the anode layer. While such pores are necessary for oxygen flow, the effective electrode-electrolyte interface at the electrode-electrolyte surface for electrical purposes is consequently reduced. Also, the existence of pores in an electrode increases substantially the sheet resistance of such an electrode.